Point is...the katana design is better for cutting, the curved blade, the long hilt for more leverage and power. It's lighter and faster. You can achieve the same result with less effort. Broad sword you have to use too much brute force and get tired quickly. When you're gassed out, you're as good as dead. Bottom line is superior design.
But then again, this is a game forum, most if not all of you ever wield a real sword (not replica) and test anything with it. It makes more sense to pose the question in a sword forum then argue with pretentious know it all fools.